FWIW, there was originally a reference to a former gatetown to Elysium that preceeded Ecstasy in my recent Dragon article, but that section was a victim of the editing process. The same section also alluded to a city of guardinals, Safehold-of-Innocence, near to Ecstasy within the shifting fringes of the Hinterlands.
The paragraph didn't make it into print, but I'll toss it out here anyway.
For that matter, Irongate is something of a planar city, since it has a number of portals in it (they make two things in Irongate: Iron, and gates).
I also forgot to mention Stormfront. It's a djinni city in the Quasielemental Plane of Lightning. The djinn there seem unusually aggressive for their kind, hunting the sapient races of the plane. [The Inner Planes, page 94]